The first prototype proved the board worked and the alternator
could generate enough current and voltage for welding. It took
up a lot of space and the old mower was badly rusted. it would
have taken a lot of work to strip down, sand prime and paint it.
I wanted something more like a portable generator.

Major components:

Craftsman Riding Mower Frame

12 HP Briggs and Stratton Engine

Custom control board

Hand-wound reactor

3 x 23,000uf/75V capacitors

Motorcraft 200A alternator

1/2" alternator pulley

Main drive and ideler pulleys from riding mower.

Ignition switch

Battery

Gast tank, approximately 1.5 gallons from riding mower.

Charge/discharge ammeter

Tweco-compatable output terminals (turned on lathe.)

Throttle control cable from riding mower.

Kill relay

Sheet metal from old combo washer./dryer.

1" x 1" x 1/8" angle iron

I started with the frame from another riding mower:

The 18HP was nice, but it was huge. I opted for a 12HP engine
that ran well and fits better within the frame. 1" angle
iron for frame. Tank and battery sit in the top.

Left is the control panel and output terminals; 3/4" conduit
used for handles. Right image is the pully setup underneath for
the alternator. The idler in the middle makes the belt cover a
longer angle around the pulleys. That helps prevent slipping.
The upper idler is spring loaded.

Here's all the parts installed for an initial test. Yes, the
wiring is a mess ;). There is a reactor coil at the center with
2 large capacitors. This helps smooth the arc and provides easier
starting in arc mode. The caps also help it delever the large
surge needed in short-arc MIG welding. Test welds show the 12HP
had plenty of power for up to 3/32 rods. It should be able to
do 130A on MIG.

Almost done. Side panels made out of sheet metal cut from an
old clothes dryer. Just needs final top cover and paint.

Just about done. Still need to paint panel. You can
see the connector for the wire feeder or footpedal below the main
panel.